This invention relates to a method of performing laser ophthamological surgery, more specifically to a technique for treating subretinal neovascularization (SRNV) with transscleral laser therapy.
The human eyeball is shown generally at 1 in FIG. 1. Subretinal neovascularization (SRNV) 6 is a growth of new blood vessels underneath the retina 3 and above the choroid 4 (See FIGS. 1 and 2). New blood vessels originating in the inner layer of choroid 4 develop between the choroid 4 and retina 3 with capillaries eventually invading retina 3 causing macular changes, degeneration, myopia, and eventually vision loss. New blood vessels growing between the pigment area of retina 3 and the sensory area of the retina 3 can hemorrhage leading to development of fibrous tissue in the retina resulting in visual impairment and even blindness. Serous exudate and fibrosis can also lead to the formation of a scar, degeneration of the retinal photoreceptors, and atrophy of the nearby retina 3 and choroid 4.
The exact reason for the vascular proliferation is unknown. Experiments have shown that the new vessels extend by proliferation of endothelial cells and pericytes, along with macrophages and actively proliferating epithelial cells.
To date there is no known pharmacological means for inhibiting or retarding the vessel proliferation. Traditional laser photocoagulation has been shown to be effective in selected cases of vasoproliferation. Argon and krypton laser photocoagulation has been most effective with most reported radomized trials using the argon blue/green laser. Krypton red lasers are also widely available, however, krypton red cannot penetrate intraretinal hemorrhage without producing inner retinal damage.
The object of photocoagulation is to use laser energy to obliterate the neovascular complex. Generally, intense photo coagulation is extended at least 100 microns beyond the parameter of the neovascular complex if the complex is more than 300 microns from the center of the retina. Once neovascularization starts, the entire membrane must be effectively photocoagulated because partial coagulation stimulates proliferation of additional blood vessels.
FIGS. 3-5 illustrate prior art techniques for performing photocoagulation. FIG. 3 illustrates a laser delivery system mounted on a slit lamp, known in the art, shown generally at 11. The laser energy generator 13 is connected to laser L via fiber optic cables 14 at laser input 15. FIG. 4 illustrates the device of FIG. 3 in use. A surgeon S seated at slit lamp 11 with a laser L is mounted on slit lamp 11 and patient P is opposite surgeon S. Surgeon S visualizes the treatment area through the slit lamp 11, activates laser L and laser energy E is delivered through the air (non-contact) and into the patient's eye. According to FIG. 5, the energy beam E travels through cornea 16 at lens 18 to the subretinal neovascularization complex 6. Laser beam E must go through retina 3 to reach the subretinal neovascular complex 6. This risks severe damage to the retina, i.e., iatrogenic loss of vision.